PKey::RSA and PKey::DSA now use the generic X.509 encoding scheme (e.g.
used in a X.509 certificate's Subject Public Key Info) when exporting
public keys to DER or PEM. Backward compatibility is ensured by (already
existing) fallbacks during creation.

OpenSSL::ASN1::Constructive#new and OpenSSL::ASN1::Primitive#new (and the
constructors of their sub-classes) will no longer force tagging to be set
to :EXPLICIT when tag and/or tag_class are passed as parameters. tagging
must be set explicitly.